Habitat amount is less important than habitat configuration for a threatened marsupial predator in naturally fragmented landscapes

Leonie E. Valentine,Dale G. Nimmo,Damian R. Michael,Judy A. Dunlop,Harry A. Moore,Mitchell A. Cowan

doi:10.1007/s10980-022-01411-1

Leonie E. Valentine, Dale G. Nimmo + Show 4 more

Open Access

https://doi.org/10.1007/s10980-022-01411-1

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Abstract

ContextThe amount and configuration of habitat are independent but tightly linked landscape characteristics which are often confounded in ecological studies. Differentiating the effects of each characteristic is critical for conservation, because the mechanisms by which they influence populations are distinct. While studies that have measured the effects of habitat amount and configuration separately have often found the former to be more important, a subset of these studies suggest habitat configuration can be vital to a species when habitat amount is low (10–30%).ObjectivesWe aimed to test the independent effects of habitat amount and configuration on the occupancy and abundance of an endangered marsupial predator, the northern quoll (Dasyurus hallucatus), which persists in naturally fragmented rocky landscapes, in which habitat amount is naturally low (i.e. typically < 30%).MethodsNorthern quolls were surveyed across 22 study landscapes that were deliberately selected such that habitat amount and configuration were uncorrelated. Northern quoll occupancy and abundance was estimated at each landscape using data collected from remote sensing cameras, and a combination of occupancy and n-mixture models.ResultsSpatial configuration of rocky habitats was more important than the amount of habitat when predicting quoll occupancy and abundance; northern quolls were less abundant in landscapes that were more fragmented. In addition, northern quolls favoured areas that were topographically rugged and received more rainfall.ConclusionsOur results support the hypothesis that the effects of habitat configuration can be strongest when habitat amount is low, and underscore the importance of aggregated patches of rocky outcrops for northern quoll conservation. The subdivision of rocky habitat, for instance through construction of mines or mining infrastructure (e.g. road, rail lines), is likely to have negative impacts on northern quoll populations.

Highlights

The relative importance of habitat amount and configuration in shaping species’ distributions and abundance has been debated for decades (Andren 1994; Fahrig 2003)
We aimed to test the independent effects of habitat amount and configuration on the occupancy and abundance of an endangered marsupial predator, the northern quoll (Dasyurus hallucatus), which persists in naturally fragmented rocky landscapes, in which habitat amount is naturally low
Across all landscapes and seasons, we recorded a total of 1004 independent northern quoll detections, a slight majority of which were recorded in the wet season (56.4%)

Summary

Introduction

The relative importance of habitat amount and configuration in shaping species’ distributions and abundance has been debated for decades (Andren 1994; Fahrig 2003). Understanding the relative influence of each is important in fragmented landscapes, where patches of ‘habitat’ exist within a matrix of less suitable or hostile “non-habitat”, and conservation planners must prioritise areas of habitat for protection or restoration (Fahrig 2003; Haddad et al 2015). In such instances, a key question is whether to maximise the overall amount of habitat—irrespective of the isolation or connectivity among habitat patches—or whether the configuration of habitat (e.g., the dispersion of habitat patches) warrants consideration (Villard and Metzger 2014). Using simulations, Fahrig (1998) found fragmentation only had an important effect on species survival when habitat cover used for breeding was less than 20%, whereas Villard and Metzger (2013) and Melo et al (2017) found configuration was most important at intermediate values of habitat amount. McGarigal and McComb (1995) showed habitat area was always more important than habitat configuration in predicting the abundance of breeding birds in north-west America, regardless of the amount of habitat present within a landscape

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